The present invention relates generally to image capturing systems, and more particularly to lens focusing devices, systems and methods used in image capturing systems.
Lenses are used in almost every image capturing system, whether that system is a film camera, a digital camera, a scanner, a copier, a facsimile machine or other system. Lenses gather light, and focus the light onto a recording medium or light sensitive component, sometimes called a detector, that generates electrical signals in response to the light. It is intuitive that correctly focusing light is critical to accurately capturing a desired image. If light is not properly focused, a blurry image will be recorded.
Three methods are commonly used to properly focus light: fixed focusing, manual focusing and automatic focusing. Fixed focusing is often used in low-end cameras, as well as in most copiers, scanners, facsimile machines, etc., due to the low cost and ease of use. Manual focusing is used in a variety of midrange to higher-end systems, and automatic focusing is predominantly used in high-end cameras and other image capturing devices that require fine image detail.
All of these focusing methods attempt to position a lens an appropriate distance from the detector, so that the light transmitted through the lens is focused on the detector. This distance is sometimes referred to as the focal length of the lens. The focal length of a lens is dependent upon the wavelength (and therefore the frequency) of light passing through the lens. For example, a single lens will focus red light and blue light at slightly different distances from the lens. In particular, red light actually refers to a portion of the electromagnetic spectrum made up of many wavelengths, and a single lens will focus each of these different wavelengths of red light at slightly different distances. Accordingly, each wavelength within the electromagnetic spectrum is focused at a different distance.
As a result, when a lens focuses light onto a detector, whether using a fixed focus system, a manually focused system, or an automatic focusing system, the lenses focal length is configured to focus a wavelength that provides a compromise focus for a set of wavelengths. In general, the compromise wavelength to which the lens is focused is chosen so that no portion of the visible portion of the electromagnetic spectrum is too far out of focus.
While this procedure has been adequate when used with a single set of wavelengths generally within the visible portion of the electromagnetic spectrum, some image capturing systems, such as film scanners, are beginning to use that portion of the electromagnetic spectrum outside of the visible portion of the electromagnetic spectrum. As a result, focusing a lens for a compromise wavelength is less effective, because of the greater difference in wavelengths between the visible and other parts of the electromagnetic spectrum. A single lens in a single position can not adequately focus this entire range of wavelengths.
Therefore, what is needed is a way to allow image capturing systems the ability to focus multiple portions of the electromagnetic spectrum with a single detector. Accordingly, the present invention comprises a device, system and method capable of focusing a first set of wavelengths of light onto a detector, and then focusing a second, different set of wavelengths of light onto the same detector. In at least one embodiment, the first set of wavelengths of light comprises predominantly visible light, and the second set of wavelengths comprises predominantly infrared light.
One embodiment of the present invention provides a lens focusing system comprising at least one lens capable of focusing at least two different sets of wavelengths of light from a scene onto a detector by altering the distance from said at least one lens to said detector. In at least one embodiment, at least one of the at least two different sets of wavelengths of light comprises predominantly visible light, and another of the two sets of wavelengths comprises predominantly infrared light.
In at least one embodiment, a first distance of the lens from the detector is determined using an automatic focusing system capable of focusing a set of wavelengths comprising primarily visible light, and a second distance of the lens from the detector is a predetermined offset from the first distance.
An alternate embodiment of the present invention provides a lens focusing system comprising a plurality of lenses capable of being interposed in an optical path between a scene and a detector. The plurality of lenses is capable of focusing at least two different sets of wavelengths of light from the scene onto the detector by moving at least one of the plurality of lenses into and out of the optical path. In at least one embodiment, the first frequency corresponds to visible light, and the second frequency corresponds to infrared.
In addition to these embodiments, the lens focusing system may be included as part of an image capturing system. The image capturing system also comprises a detector capable of generating electrical signals in response to light, at least one illumination source capable of providing illumination in the infrared portion of the electromagnetic radiation spectrum, as well as at least one illumination source capable of providing illumination in the visible portion of the electromagnetic radiation spectrum.
An advantage of at least one embodiment of the present invention is that an automatic focusing system can be easily adapted for infrared focusing simply by using a predetermined offset to a focusing element""s position.
An advantage of at least one embodiment of the present invention is that a sharper images can be recorded, because the lens is in focus for both visible and infrared scans.